Systems that use storage batteries have been put into practical use in order to effectively utilize renewable energy and nighttime power. These storage batteries are typically nickel hydrogen storage batteries or lithium-ion storage batteries, which have excellent properties such as charge and discharge efficiency. However, as in the case of lead storage batteries, it can be difficult to manage the remaining power in these storage batteries using voltage. Therefore, nickel-hydrogen and lithium-ion storage batteries have been developed with power-level gauges, and these power-level gauges are used to manage the remaining power in storage batteries and deterioration of the storage batteries. However, errors are known to occur in power-level gauges, so a means has been proposed to periodically correct errors that have occurred in these gauges (recalibration). A means for correcting errors that have occurred in power-level gauges has been disclosed in Japanese Laid-open Patent Publication No. 2008-271759 (A).
In the method disclosed in Japanese Laid-open Patent Publication No. 2008-271759 (A), a rechargeable battery is forcibly discharged, the capacity (lower capacity) of the rechargeable battery is corrected after the discharge, the rechargeable battery is charged, and the capacity (upper capacity) of the rechargeable battery is corrected after the charge to complete the recalibration.
Also, the power storage systems for storing power for renewable energy and nighttime power often include a plurality of storage batteries in order to be able to store a larger amount of power than is consumed by the expected load. This enables the power storage system to operate when there is insufficient daylight or when a power outage occurs. It also extends the life of the storage batteries because the depth of discharge is not very high.